The present invention relates to a switch for controlling the operation of an electrical appliance.
The electrical switch of a known type includes a casing, two fixed contacts and a moving contact which has opposite ends for short-circuiting the fixed contacts to close the switch upon movement by an operating member through the action of a spring. In case that the spring malfunctions and in particular when it is broken, the moving contact may stay in contact with the fixed contacts. This situation is undesirable and not safe.
The invention seeks to mitigate or at least alleviate such a problem by providing an improved electrical switch of this type in general.
According to the invention, there is provided an electrical switch comprising a casing, and at least two fixed contacts and a corresponding moving contact in the casing. The moving contact has two parts contactable with the fixed contacts respectively thereby closing the switch. An operating member is supported for movement relative to the casing for moving the moving contact to close the switch. Resilient means acts upon the moving contact such that its two parts are inclined at an acute angle relative to the fixed contacts, with at least one of the parts being spaced apart from the corresponding fixed contact while the switch is open. The moving contact is movable such that said at least one or both of its parts comes or come into contact with the corresponding fixed contact or contacts against the action of the resilient means.
Preferably, the moving contact has one side facing the fixed contacts and an opposite side on which the resilient means is provided.
More preferably, the resilient means comprises a compression coil spring.
In a preferred embodiment, the electrical switch includes a carrier movable by the operating member and carrying the moving contact and the resilient means for simultaneous movement. The carrier includes an inclined portion lying against which the moving contact is acted upon by the resilient means to incline at said acute angle relative to the fixed contacts.
More preferably, the fixed contacts are spaced apart by a gap, and the carrier is supported for movement in the gap such that its inclined portion is movable at least partially beyond the fixed contacts to allow the two parts of the moving contact to contact with the corresponding fixed contacts.
More preferably, the carrier includes a recess having opposite, first and second ends and locating the moving contact and the resilient means. The moving contact lies against the first end that being the inclined portion and the resilient means co-acts between the moving contact and the second end.
In a specific construction, the electrical switch includes two pairs of said fixed contacts and two corresponding said moving contacts movable simultaneously by the operating member for operation.
In general, the electrical switch may include a sliding carrier carrying the moving contact and the resilient means for simultaneous movement, a slider movable by the operating member for in turn moving the carrier, and an over-centre pivotal spring co-acting between the carrier and the slider such that the carrier and the slider are slidable in opposite directions.
Slightly more specifically, the operating member is supported for pivotal movement and is connected to the slider by means of a link for moving the slider. The electrical switch may be a normally-open switch, in that the operating member is resiliently biassed by a spring towards an inoperative position.
In particular, the electrical switch may be a trigger switch for use in an electric power tool.
According to a slightly different aspect of the invention, there is provided an electrical switch comprising a casing, and at least two fixed contacts and a corresponding moving contact in the casing. The moving contact has two parts contactable with the fixed contacts respectively thereby closing the switch. An operating member is supported for movement relative to the casing for moving the moving contact to close the switch. The moving contact is supported with its two parts inclined at an acute angle relative to the fixed contacts under the action of resilient means such that at least one of its parts is spaced apart from the corresponding fixed contact whale the switch is open. The moving contact is movable against the action of the resilient means to have its two parts turning through said acute angle until both parts are in contact with the corresponding fixed contacts.